1. Field of the Invention
This invention relates to a technique for automatically recording images such as still images and moving images.
2. Description of the Related Art
A security system for automatically recording images such as still images and moving images by a security camera and recording the images on a recording medium is conventionally known. Although the quality of the recorded image is desirably as high as possible, it is also desirable to increase the recording time as long as possible. However, there is a tradeoff relationship between the image quality and recording time, so it is generally difficult to achieve high image quality and long-term recording simultaneously.
Accordingly, a security system which performs recording at high resolution in scenes regarded as important and performs recording at low resolution in scenes not regarded as important is proposed (Japanese Patent Laid-Open No. 2002-016877). This security system determines the importance of a scene on the basis of the motion of an object.
To perform monitoring for a longer period of time, it is only necessary to record no images in (normal) scenes with no motion, and record images in (abnormal) scenes with motion. This makes it possible to preserve the recording medium.
In a security system which records an image only when an abnormality is detected, however, no images are recorded in normal scenes, so nothing may be recorded if the detection of an abnormality has failed.
A monitoring environment in which the detection of an abnormality easily fails is principally an environment in which the brightness or light intensity is low. Especially when the number of image pickup elements of an imaging device is increased to increase the resolution, the effective light receiver area per image pickup element is normally reduced. Since the sensitivity lowers accordingly, the possibility of an abnormality detection failure increases more and more.